Motion artifacts have long been a problem during the measurement of biopotentials, particularly in long-term electrocardiogram (ECG) monitoring of coronary care patients and in exercise (stress) ECG's. Motion artifacts can be defined as motion induced fluctuation of the electrical potential across the skin of the patient. Motion artifacts manifest themselves as electrical interference which is often superimposed on the desired biopotential signal and minimizes the usefulness of the biopotential signal for diagnostic and clinical purposes. Motion artifacts are generally caused by the movement of the patient relative to the electrode applied to the patient's skin, thereby disturbing the skin potential and creating extraneous readouts on the ECG monitor which either mask or cause a shift in the baseline of the desired biopotential signal.
It is well known that light abrasion of the skin reduces the electrical potential and minimizes the impedance of the skin of the patient, thereby reducing motion artifacts and improving signal or trace quality of the biopotential signal. Although there are many commercially available surface mounted electrodes for cardiac monitoring described in the literature, reliable signals or trace results from these electrodes in highly dependent on adequate skin preparation prior to application of the electrodes. Proper skin preparation is time consuming because typical stress electro-cardiograms usually require between three and 12 electrodes and typically use about 10 electrodes. Skin preparation is normally necessary to remove the epidermal layer of the skin of the patient and is carried out in a variety of ways. The most common method of preparing the skin is to rub the patient's skin with a gritty material contained in a carrier or to rub the patient's skin with a rough surfaced material to which an antiseptic such as alcohol or other solvent is applied. After briskly rubbing the skin, the skin is dried and again rubbed with a dry cloth. If, after the electrodes are applied, a proper signal or trace is not obtained from one or more of the electrodes, the malfunctioning electrodes must be identified, removed and the skin must be prepared again. The electrodes are then reapplied to the skin of the patient, and this procedure is repeated until an adequate and accurate signal is received from each electrode. The effectiveness of the skin preparation is highly dependent on the technique used as well as the level of skill of the person preparing the skin. Predictably, the effectiveness of the skin preparation in this uncontrolled manner is highly variable between electrode locations as well as between patients.
U.S. Pat. Nos. 4,274,419 and 4,311,152 are owned by the assignee of the present invention and disclose a surface mounted medical electrode suitable for recording biopotential measurements in which the electrode is first applied to the patient, and then the skin of the patient is prepared. Such an approach markedly reduces the time consumed in the application of electrodes for recording biopotential events. Also, more reliable, accurate and uniform signals are obtained since the amount and type of skin preparation for each electrode is generally uniform.